Excessive Clotting Disorders

Laboratory Tests

Initial testing is usually performed to determine if a person has or has had a blood clot (thrombotic episode) and, if so, to help determine the person's risk of a repeat thrombotic episode. Although it may be fairly simple to identify that a person has a clot, identification of the underlying cause may take more time and effort. This is because several of the diagnostic tests that need to be done are affected by an existing or recent blood clot and by any anticoagulant therapy that is given. Often, the doctor may have to order a few tests and treat the person's existing blood clot first. Several weeks or months later, when he is able to take the person off of anticoagulant therapy, the doctor can order other tests to finish his evaluation of the cause of the clotting. Follow-up testing is important in helping to determine a person's risk of developing recurrent blood clots.

The table below lists some of the tests in alphabetical order. For detailed information about each test, click on the name of the test to go to the specific article.

Not all of the tests listed in the table are needed for each person with excessive clotting disorders. If somebody has been diagnosed as having a blood clot in a vein (venous thrombosis), the first step is to rule out obvious causes of acquired thrombosis, including malignancy, major surgery (e.g., orthopedic), trauma, immobilization, congestive heart failure, myeloproliferative neoplasms, or nephrotic syndrome. Routine tests including PTT, PT, fibrinogen activity, and D-dimer are generally performed. As to other tests, the following general guide is used to determine what tests should be performed based on patient age and personal and family history.

If a person has a first episode of venous thrombosis at an age older than 50 without known acquired risk factors and there is no personal or family history of recurrent episodes, then a limited test panel is often performed, including factor V Leiden mutation and prothrombin gene G20210A mutation, antiphospholipid antibodies (including lupus anticoagulant) and homocysteine.

The medical and family histories plus laboratory testing may reveal that a person has more than one factor or condition that increases their risk of excessive clotting, and the resulting risk can be cumulative. For example, a person whose laboratory tests indicates the presence of Factor V Leiden mutation will likely be at greater risk if they also are bed-ridden or hospitalized for some time (prolonged immobilization).

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This article was last reviewed on July 14, 2011. | This article was last modified on July 21, 2013.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.